Method of coating with tungsten carbide



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H. s. HATFIELD METHOD OF COATING WITH TUNGSTEN CARBIDE Filed July 14, 1942 Patented Feb. 3, 1948 UNITED STATES PATIENT OFFICE.

METHOD or COATING WITH TUNGSTEN CARBIDE Henry Stafford Hatfield, Hildershani, England Application July 14, 1942, Serial No. 450,941

In Great Britain July 31,1941

Section 3, Public Law 690, August 8, 1946 Patent expires July 31, 1961 sistance to corrosion or abrasion, electrically important properties such as photo-electric or secondary electron emission, and the like. The beam of rays, focussed on the surface, heats it and the coating material (supplied before or during the application of the rays, very rapidly to the point at which they fuse together. Such material may first be applied to the surface by any suitable means in the form of a coating, and then be incorporated by exposure to the rays. Or it may be injected in the form of a fine powder into the beam of rays, or be evaporated by suitable means so as to be deposited on the surface. It is a common practice to fuse a thin layer of material onto the surface of a body by means of a blowpipe, the material being previously applied to the surface, or fed to it simultaneously with the flame. This invention consists essentially in the use as a new'sort of blowpipe of focussed electric rays. This allows a very high temperature to be attained so quickly that amalgamation of the coating with the surface occurs before the heat penetrates.

For example, hard steel parts may be coated with very finely powdered tungsten or other hard metal carbide, and exposed to the beam. Alternatively, the finely powdered carbide may be fed mechanically into the beam as it is made to impinge on the surface. The metal may also be coated with tungsten, or may contain it in the form of an alloy, and the carbide be afterwards formed from carbon powder applied under the heat of the beam.

6 Claims. (Cl. 117-433) results in a strong field very close to the surface I will describe two ways in which the standard forms of apparatus used for producing X-rays by the action of a beam of cathode rays upon a target, may be adapted with little change to serve the purposes of this invention. Figure 1 of the accompanying drawing represents in section the manner of using a hot-cathode apparatus, Figure 2 the adaptation of a cold-cathode apparatus, such as was in general use for generating X-rays'before the invention of the hot cathode. Each has its advantages for the purpose of this invention, for the following reasons:

In the hot cathode tube, the electrons escape from the cathode into an electrostatic field which extends to the anode, the applied high voltage? being distributed over this space, so that it is necessary for the target to be situated near the cathode, and to be the anode. There is therefore a very strong electric field at the surface of the target, which tends to cause any loosely adherent matter to be thrown off. In the cold cathode arrangement, the applied high potential of the cathode, and the electrons emitted from the latter are therefore given a very high velocity in a direction at right angles to the surface of the cathode, flying to a focus at the target, which may be at any desired distance from the cathode. In the cold cathode tube, the presence of gas is necessary; 0.001 mm. of hydrogen gas is usually chosen. This is an'advantage in that a very high vacuum is notnecessary; on the other hand, the pressure of the gas has a great efiect upon the amount and velocity of the electrons emitted. Since in carrying out this invention we are necessarily working with demountable apparatus,

that is, apparatus in which the vacuum has to be broken from time to time, there is no dimculty, with modern pumps and appliances, in adjusting the gas pressure as required. In the cold cathode tube, there is only a small electrostatic'field near' the surface of the target, and this may be almost abolished by a suitable screen.

A A hot-cathode arrangement suitable for coat-1 ing small steel parts, such as the working faces of limit gauges, with tungsten carbide, is shown inFig. 1. The cathode filament l is enclosed in a metal bell 2, open below, and having inits centre a small vessel 3,;made of tungsten or molybdenum. This vessel has a perforated bottom, and contains tungsten carbide powder, which, passes through the perforations at the bottom, when the apparatus is subjected to vibration, at.

a rate dependent upon the intensity of the vibration. 4 is the part to be coated, such as a small cylinder of steel intended for a limit gauge. It is connected to the positive end of the high tension supply, which is of any standard form as used for X-ray work. The apparatus used for producing vibration may also be of any standard type used for causing powders to pass through screens.

The waste heat from the cathode serves to heat the tungsten powder; the target may also be heated in the manner familiar in the degassing of vacuum tubes, by subjecting it to a high-frequency field. Preheating shortens the period of, 

